This invention relates generally to fabrication methods for producing thin film electrochemical sensors of the type used, for example, in subcutaneous or transcutaneous monitoring of blood glucose levels in a diabetic patient. More specifically, this invention relates to an improved fabrication method wherein thin film sensors are formed on a rigid flat substrate by contact mask photolithography or the like, without requiring attachment of the sensors to the substrate.
Thin film electrochemical sensors are generally known in the art for use in a variety of specialized sensor applications. Such thin film sensors generally comprise one or more thin conductors applied by photolithography mask and etch techniques between thin layers of a nonconductive film material, such as polyimide film. The conductors are shaped to define distal end sensor tips having an appropriate electrode material thereon, in combination with proximal end contact pads adapted for conductive connection with appropriate electronic monitoring equipment. In recent years, thin film sensors of this general type have been proposed for use as a transcutaneous sensor in medical applications. As one example, thin film sensors have been designed for use in monitoring blood glucose levels in a diabetic patient, with the distal end sensor electrodes positioned subcutaneously in direct contact with patient blood.
In accordance with known photolithographic fabrication techniques, thin film sensors have been produced by sequential buildup of the sensor layers on a flat and rigid substrate, such as a glass plate. A base layer of insulative material is formed on the substrate, typically by applying the base layer material onto the substrate in liquid form and thereafter spinning the substrate to yield the base layer of thin, substantially uniform thickness. These steps are repeated to build up the base layer of sufficient thickness, followed by a sequence of photolithographic mask and etch steps to form the conductors. A cover layer of insulative material is then applied, and the resultant sensors are stripped from the substrate. However, this stripping step must be performed carefully in order to separate the finished sensors from the substrate without damage. Unfortunately, the initial step of spin forming the base layer on the substrate causes the base layer to be firmly adhered to the substrate, such that separation of the finished sensors from the substrate is both costly and time consuming, thereby undesirably increasing the manufactured cost of thin film sensors.
There exists, therefore, a need for improvements in methods for producing thin film electrochemical sensors, particularly with respect to reducing sensor production time and cost by facilitating removal of finished sensors from a flat substrate. The present invention fulfills these needs and provides further related advantages.